1. Field of the Invention
The present invention relates to an electrical connection between a radially inner and a radially outer member, for example, in a housing assembly of a wellhead of an oil or gas field.
2. Description of the Related Art
Electrical connections are required in housing assemblies for high power circuits for running downhole equipment such as pumps and heating coils, and for electrical signals to and from downhole equipment. Such electrical connections are conventionally made through the top of the tubing hanger once the tubing hanger is landed in a housing or wellhead. The space available for the connections is therefore limited. This may result in the production bore being off-centre which has serious operational implications in ensuring equipment is correctly aligned. Furthermore, the blow out preventer has to be removed for access to the top of the tubing hanger. The tubing hanger then provides the only barrier, which causes a safety problem if the well is live.
The electrical connection must pass through a pressure boundary to the tubing hanger. In the case of a power core, full insulation is needed. As good insulators have generally poor sealing properties, sealing at the pressure boundary at the well temperature is difficult.
According to the present invention, an assembly providing an electrical connection across an interface between a radially inner member and a surrounding radially outer member, comprises a sealed enclosure between the inner and outer members; a cable which leads to the enclosure and is fixed and sealed to a wall of the enclosure, and which has at least one conducting core; an electrical coupling element within the inner member; and a shuttle which is reciprocatable radially inwardly from a disconnected position wholly within the outer member to a connected position in which the shuttle makes an electrical connection from the conductor core to the electrical coupling element.
As the connection is made across a peripheral surface in a radial plane, it does not have to be through the top of the inner member, e.g. a tubing hanger. Therefore the space limitation of the prior art is avoided. Furthermore, when the invention is applied to the housing of a wellhead assembly, it eliminates the need to remove the blow out preventer.
It is the shuttle which bridges the gap across the enclosure between the inner and outer members and therefore prevents damage to the cable which is not exposed in the potentially hostile pressurised region between the two members. No electrical cables or components are required to move through a pressure barrier so that make up can be achieved in a constant volume void irrespective of the pressure.
As the shuttle does not have to contain pressure, there is no problem achieving an insulated connection.
In one embodiment, generally suitable for an electrical signal, a connecting cable connected to the cable is coiled within the enclosure and is fixed to the shuttle. The connecting cable may be an extension of the cable core. When the electrical connection is made up, the coil is simply extended.